Aircraft lighting systems are used to provide lighting for various purposes. Some systems provide illumination of instrumentation. Some systems illuminate cabin spaces. Some systems are for external lighting. Some systems provide overhead illumination of passenger seating areas to facilitate reading. Light Emitting Diode (LED) arrays are used to provide illumination for some of these lighting systems. LED arrays can require large power controllers to control the hue and brightness. Such power controllers can be located near each individual lighting source, resulting in a large number of such controllers. Having controllers distributed throughout an aircraft can contribute weight to the aircraft and add expense to the cost of the aircraft.
The intensity of light emission from LED lighting arrays changes in response to an applied power to the LED lighting array. As the applied power is increased, the intensity of light emission usually increases. Some LED lighting arrays emit a light whose color is also a function of the power consumed by the LED lighting array. For example, the color of the emitted light can change in response to a change in the applied voltage to the LED lighting array. People expect that some lighting systems will have a specific color. For example, when reading, people expect overhead illumination to be within a predetermined range of colors called “white light.”
Because both intensity and hue are functions of the voltage and current applied to an LED lighting array, control of both intensity and hue are performed using pulsed methods. The voltage and current levels are determined by a color specification. Then a duty cycle is determined by an intensity specification. The frequency rate at which these pulses are applied to an LED lighting array is bounded by two different concerns or hazards. If the pulse rate is too low, a human will perceive the LED lighting array to be undesirably flickering. If the pulse rate is too high, conducted and/or radiated emissions may cause undesirable coupling to sensitive airplane instrumentation.